When the water should be changed
Lucky bamboo is tough! It can survive for months, even years, without fresh water and even in stagnant, green slimy water fit only for alligators and turtles. Then, it will die.
Fresh water is important to the lucky bamboo in many ways. It replenishes the nitrogen and oxygen levels. Keeps root rot from developing. Fresh water is a source for trace elements needed to keep the plant healthy. It makes it hard for bacteria, mold, fungus and insects to get a hold on the plant. Beside these benefits, fresh water smells better.
How often to change the water is a function of the size of the vase, filler material, temperature and the number of plants, but not complicated. Smaller vases need to be changed more often than large vases. Those with filler materials, rock or glass, contain less water and need to be changed more than those without fillers. Adding a little water from time to time, will keep the roots covered but if the stems feel slimy or begin to smell like your gym socks, you have waited too long.
Usually, changing the water at set intervals is desirable. Say every Saturday or third Thursday, the main point is not to forget and stress the plant.